Multi-dimensional RF Pulses for MRI Spatial Encoding
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Solution Overview
Problem
Conventional MRI and MRS methods face delays in signal acquisition due to spatial encoding performed post-excitation, which is inadequate for measuring magnetic resonance signals with short transverse relaxation times and introduces spatial inaccuracies due to gradient pulse imperfections.
Innovation Solution
The method involves performing phase encoding during the excitation period using multi-dimensional RF pulses, allowing for simultaneous spatial encoding of an interrelated region, thereby reducing acquisition delays and enhancing spatial resolution by using a predetermined k-space trajectory and phase encoding scheme.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spatial encoding is performed post-excitation using conventional gradient pulses, then spatial localization can be achieved, but acquisition delay increases and measurement precision deteriorates for short transverse relaxation times
Solution Approach 1:
The patent applies preliminary action by performing spatial encoding during the excitation period itself rather than after excitation. The multi-dimensional RF pulse incorporates phase encoding gradients that encode spatial information concurrently with spin excitation, eliminating the post-excitation encoding delay and enabling immediate signal acquisition for short T2* species.
Solution Approach 2:
The patent merges the excitation and spatial encoding operations into a single integrated process. The multi-dimensional RF pulse combines excitation functionality with phase encoding gradients in the readout direction, consolidating what were previously separate operations into one simultaneous action that reduces total measurement time.
2Measurement precision
If conventional gradient pulses are used for spatial encoding, then spatial localization is achieved, but imaging accuracy deteriorates due to gradient pulse imperfections
Solution Approach 1:
The patent uses frequency encoding as a copy or alternative method of spatial encoding that is less sensitive to gradient imperfections. By encoding spatial information in the frequency domain through the RF pulse spectrum rather than relying solely on gradient-induced phase evolution, the method creates a redundant encoding pathway that is more robust to gradient pulse errors.
3Productivity
If multi-dimensional RF pulses with phase encoding during excitation are used, then acquisition delay is reduced and spatial resolution is enhanced, but device complexity increases
Solution Approach 1:
The patent extends spatial encoding from the traditional time domain (post-excitation phase encoding) into the frequency domain by incorporating phase encoding gradients during the RF excitation pulse itself. This dimensional shift allows spatial information to be encoded in the spectral dimensions of the RF pulse, enabling faster acquisition without proportionally increasing system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the delay between excitation and data acquisition, enabling spatially resolved measurement of magnetic resonance signals with short transverse relaxation times and improving imaging accuracy by minimizing errors from gradient pulse imperfections.
Implementation Method 1
the nuclear spins of the object under investigation, which are oriented in this fashion, are excited through irradiation of electromagnetic radio frequency (RF) pulses using one or more RF transmitting antennas, to perform precession motions, the frequencies of which are proportional to the local magnetic field strengths
Implementation Method 2
the precession motions of the nuclear spins are superposed with a spatial encoding for all spatial directions to be spatially resolved, through time-variant superposition of magnetic gradient fields G x , G y , G z , which are generated by a gradient system
Implementation Method 3
The transverse component of magnetization associated with the precessing nuclear spins induces voltage signals in one or more RF receiver antennas that generally surround the object under investigation
Data Source
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AI summary
A method for determining the spatial distribution of magnetic resonance signals from an imaging area, wherein nuclear spins are excited in a spatially encoded fashion through multi-dimensional RF pulses, is characterized in that in a definition step, a resolution grid with resolution grid cells is predetermined, and in accordance with a predetermined phase encoding scheme, an excitation pattern is defined for each phase encoding step, in which the amplitudes within the imaging area are set in accordance with a predetermined distribution identically for each phase encoding step, the amplitudes of the residual resolution grid cells are set to zero, and the phases of the resolution grid cells within the imaging area are set in accordance with the phase encoding scheme, in a preparatory step, the amplitude and phase behavior of the RF pulses to be irradiated is calculated in accordance with a predetermined k-space trajectory for each defined complex excitation pattern of the phase encoding steps and for each transmitting element, in an execution step, the nuclear spins are repeatedly excited, such that spatial encoding is performed within the imaging area during excitation of the nuclear spins.